1. Field of the Invention
The present invention relates to an organic light emitting display device and a driving method thereof, and more particularly, to the luminance adjustment in an organic light emitting display device.
2. Description of the Related Art
Among flat panel display devices, an organic light emitting display device displays an image by using organic light emitting diodes (OLEDs) in which emissive electroluminescent layer is a film of organic compound which emits light in response to an electric current using a low power consumption. The layer of organic semiconductor is situated between two electrodes and has excellent light emitting efficiency, luminance, and angle of view.
In general, light emitting display devices are classified into a passive matrix organic light emitting display device (PMOLED) and an active matrix organic light emitting display device (AMODED) according to how organic light emitting diodes are driven.
The passive matrix type corresponds to a method of forming a positive electrode and a negative electrode such that they are perpendicular to each other, then selecting and driving a negative electrode line and a positive electrode line. The active matrix type corresponds to a driving method in which a thin film transistor and a capacitor are integrated in each pixel to maintain a voltage by a capacity of a capacitor. The passive matrix type (PMOLED) has a simple structure and is inexpensive, but is difficult to realize a large-sized or high precision panel. On the other hand, the active matrix type (AMOLED) can realize a large-sized and high precision panel, but a control method thereof is technically difficult and expensive. In the aspects of resolution, contrast, and operating speed, the active matrix organic light emitting display devices (AMOLEDs) which select and switch on unit pixels are mainly used.
Meanwhile, factors for improving display quality of an organic light emitting display device may include gamma setting. The gamma setting is a correlation between display luminance and grayscale data, which is defined according to a gamma curve. A very accurate gamma setting is necessary for the organic light emitting display device to maintain a stable display quality. Gamma setting errors are occasionally generated by various factors such as dispersion of components, a cell gap of a liquid crystal panel, a change in thickness of a color filter, and a driving voltage in an actual organic light emitting display device. If an error is generated in the gamma setting, a deviation is generated between the actual display luminance and the display luminance due to the grayscale data. In order to minimize the deviation, multi time programming (MTP) which programs a reference gamma voltage in real time is performed. A reference gamma voltage is a voltage input to a driving circuit which generates a data signal for determining display luminance. According to the grayscale data, the driving circuit generates a data signal by using a reference gamma voltage, and the light emitting elements emit light in response to the data signal. Thus, if the reference gamma voltage is changed, the display luminance of the organic light emitting display device is also changed.